/*
 * Copyright 2002-2017 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.http.converter;

import java.io.IOException;
import java.nio.charset.Charset;
import java.nio.charset.StandardCharsets;
import java.util.ArrayList;
import java.util.List;

import org.springframework.http.HttpInputMessage;
import org.springframework.http.HttpOutputMessage;
import org.springframework.http.MediaType;
import org.springframework.lang.Nullable;
import org.springframework.util.Assert;
import org.springframework.util.StreamUtils;

/**
 * Implementation of {@link HttpMessageConverter} that can read and write strings.
 *
 * <p>By default, this converter supports all media types ({@code &#42;&#47;&#42;}),
 * and writes with a {@code Content-Type} of {@code text/plain}. This can be overridden
 * by setting the {@link #setSupportedMediaTypes supportedMediaTypes} property.
 *
 * @author Arjen Poutsma
 * @author Juergen Hoeller
 * @since 3.0
 */
public class StringHttpMessageConverter extends AbstractHttpMessageConverter<String> {

    public static final Charset DEFAULT_CHARSET = StandardCharsets.ISO_8859_1;


    @Nullable
    private volatile List<Charset> availableCharsets;

    private boolean writeAcceptCharset = true;


    /**
     * A default constructor that uses {@code "ISO-8859-1"} as the default charset.
     *
     * @see #StringHttpMessageConverter(Charset)
     */
    public StringHttpMessageConverter() {
        this(DEFAULT_CHARSET);
    }

    /**
     * A constructor accepting a default charset to use if the requested content
     * type does not specify one.
     */
    public StringHttpMessageConverter(Charset defaultCharset) {
        super(defaultCharset, MediaType.TEXT_PLAIN, MediaType.ALL);
    }


    /**
     * Indicates whether the {@code Accept-Charset} should be written to any outgoing request.
     * <p>Default is {@code true}.
     */
    public void setWriteAcceptCharset(boolean writeAcceptCharset) {
        this.writeAcceptCharset = writeAcceptCharset;
    }


    @Override
    public boolean supports(Class<?> clazz) {
        return String.class == clazz;
    }

    @Override
    protected String readInternal(Class<? extends String> clazz, HttpInputMessage inputMessage) throws IOException {
        Charset charset = getContentTypeCharset(inputMessage.getHeaders().getContentType());
        return StreamUtils.copyToString(inputMessage.getBody(), charset);
    }

    @Override
    protected Long getContentLength(String str, @Nullable MediaType contentType) {
        Charset charset = getContentTypeCharset(contentType);
        return (long) str.getBytes(charset).length;
    }

    @Override
    protected void writeInternal(String str, HttpOutputMessage outputMessage) throws IOException {
        if (this.writeAcceptCharset) {
            outputMessage.getHeaders().setAcceptCharset(getAcceptedCharsets());
        }
        Charset charset = getContentTypeCharset(outputMessage.getHeaders().getContentType());
        StreamUtils.copy(str, charset, outputMessage.getBody());
    }


    /**
     * Return the list of supported {@link Charset}s.
     * <p>By default, returns {@link Charset#availableCharsets()}.
     * Can be overridden in subclasses.
     *
     * @return the list of accepted charsets
     */
    protected List<Charset> getAcceptedCharsets() {
        List<Charset> charsets = this.availableCharsets;
        if (charsets == null) {
            charsets = new ArrayList<>(Charset.availableCharsets().values());
            this.availableCharsets = charsets;
        }
        return charsets;
    }

    private Charset getContentTypeCharset(@Nullable MediaType contentType) {
        if (contentType != null && contentType.getCharset() != null) {
            return contentType.getCharset();
        } else {
            Charset charset = getDefaultCharset();
            Assert.state(charset != null, "No default charset");
            return charset;
        }
    }

}
